Optical networks include Synchronous Digital Hierarchy (SDH)/Synchronous optical networks (Sonet), wave-length switched networks, and etc. A traditional optical network is a system based on centralized management and connection services between nodes of the network are implemented by way of permanent connection. The path of connection is pre-calculated by the management plane based on the connection requirement and the availability of network resources, then cross-connection commands are sent to nodes on the connection path via Network Management Interface-Transport (NMI-T) to carry out unified designation and assignment, and eventually, accomplish the establishment of a communication channel. The approach of permanent connection had good effects in the early development of optical network because the design is simple and cost is low. However, the setup, maintenance, and release of optical connection by the approach of permanent connection require the involvement of human work or network management system. With the continuing growth of traffic data, this approach of connection is no longer able to meet the dynamic and flexible requirement of an optical network system.
The key to solve this problem is the implementation of dynamic optical switching. That is why ITU-T has put forward the architecture of Automatic Switching Optical Network (ASON), which adds a control plane to a traditional optical network and puts forward the concept of switched connection. According to this idea, a node in an optical network will first obtain the link connection relations of this node with other nodes by the link discovery technique, then issue the states of node and links through the control plane, and receive the state issuance of other nodes in the network. Eventually, every optical node will have a “network map” giving a description of the accurate topology of the network and including various information about nodes, links, and resources. When a node is requested by a client or management system to establish a connection, the node will first calculate a path using the information of the “network map” combined with a certain algorithm of routing, and then drive the nodes on the path by signaling protocols to establish the cross-connection. When a network connection is dynamically created or released, or a failure brings about changes in the resources of links, related nodes will issue in time updated states of node and links to achieve re-synchronization of the “network map”. In ASON, if the connection request received by a node comes from a client device or proxy, the connection created is referred to as switched connection; if the request comes from network management system, the connection created is referred to as soft permanent connection. In this specification, switched connection and soft permanent connection are both referred to as switched connection except otherwise specified. If a switched connection or a soft permanent connection is cut off when a failure occurs in the network, e.g. a link disconnects or a node fails, the control plane will be able to re-create the routing of connection dynamically and restore the traffic. An optical network with this approach of switched connection is of dynamic and flexible characteristics and is capable of meeting the requirement of growing data traffic.
Though the approach of switched connection has many advantages, it is a long process of evolution to upgrade a traditional supply-based optical network into an ASON, for it is an enormous project of system engineering involving the upgrading of network equipment, network management system, operating and supporting systems as well as other aspects of the network. In the present process of transition, the control plane is implemented only on some nodes. Even on these “intelligent” nodes where the control plane has been implemented, manually provided connections will not disappear immediately and permanent connections and switched connections will co-exist in the network. When permanent connections and switched connections co-exist in a network, network resources are usually allocated by the management plane to the connections, respectively and it is not easy to change the allocation thereafter. However, it is often not possible for the static allocation of resources to satisfy the changing traffic of an optical network. It is often necessary for an operator to make migration between a permanent connection and a switched connection to re-allocate the resources occupied respectively by the two modes of connection and make use of the different characteristics thereof.
In the prior art, however, no method of migration between a permanent connection and a switched connection is provided. When it is needed to make such a migration, the migrated connection has to be released at first, and then a connection of the required mode can be created using the resources from the released connection. This approach of migration may cause a disruption of the traffic, damages to the data in network transmission, problems to the operation of service, as well as inconvenience for the operator, and may further affect the network evolution to ASON.